Field of the Invention
The present invention relates to a control apparatus for controlling a controlled object having a response lag characteristic.
Description of the Related Art
Conventionally, as a control apparatus, there has been known one disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2005-171893. This control apparatus controls a variable nozzle type turbocharger as a controlled object. This control apparatus calculates a target boost pressure epimtrg according to operating conditions of the engine, and feedback-controls an actual boost pressure epim such that the actual boost pressure epim becomes equal to the target boost pressure epimtrg, using a feedback control algorithm.
With this feedback control algorithm, a boost pressure difference epimdlt, which is a difference between the actual boost pressure epim and the target boost pressure epimtrg, is calculated, and a feedback control term epvnpmfb is calculated based on the boost pressure difference epimdlt, as a total sum of a proportional term epvnpmp, an integral term epvnpmi, and a derivative term epvnpmd, by a PID control method. Further, a sum epbnbse+epvnpmfb of the feedback control term epvnpmfb and a basic value epbnbse of boost pressure is compared with a predetermined minimum limiting value epvnpmin, and then the larger one of them is compared with a predetermined maximum limiting value epvnpmax, whereby the larger one of them is set as a final opening epvnfin. Then, the actual boost pressure epim is feedback-controlled such that the actual boost pressure epim becomes equal to the target boost pressure epimtrg by controlling supply current to a DC motor according to the final opening epvnfin.
On the other hand, in calculation of the integral term epvnpmi, when predetermined update inhibiting conditions are satisfied in a transient operating condition of the engine, an update of the integral term epvnpmi is inhibited, and the integral term epvnpmi is maintained at the immediately preceding value thereof. This is for suppressing an overshoot of the actual boost pressure epim, because, in the case of the variable nozzle type turbocharger, the actual boost pressure epim has a characteristic of being liable to overshoot with respect to the target boost pressure epimtrg due to the response lag, and this problem becomes more conspicuous in a transient operating condition of the engine.
Further, the present applicant has already proposed a control apparatus disclosed in the Publication of Japanese Patent No. 4282572. This control apparatus controls a variable cam phase mechanism as a controlled object, and the variable cam phase mechanism changes a cam phase CAIN as a phase of an intake cam with respect to a crankshaft of the engine. In general, in a variable cam phase mechanism, the cam phase CAIN is liable to delay in following up a target value or overshoot the target value due to a response lag of the variable cam phase mechanism.
In order to compensate for the response lag characteristic of the variable cam phase mechanism, in the control apparatus disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2005-171893, a control input Ucain to the variable cam phase mechanism is calculated using a control algorithm to which are applied a response-specifying control algorithm and an adaptive disturbance observer and a discrete-time system model defining the relationship between the control input Ucain to the variable cam phase mechanism, the cam phase CAIN, and a disturbance estimated value c1. More specifically, the control input Ucain is calculated as the sum of an equivalent control input Ueq and a reaching law input Urch, and the equivalent control input Ueq is calculated such that the cam phase CAIN, the target value of the cam phase CAIN, and the disturbance estimated value c1 are included therein as variables. In short, the equivalent control input Ueq is calculated by a deadbeat control method as a feedforward control term (feedforward control input) for causing the controlled variable to follow up the target value while compensating for the response lag characteristic of the variable cam phase mechanism.
In the case of controlling the variable cam phase mechanism using the control input Ucain calculated as above, the effect of disturbance compensation by the disturbance estimated value c1 makes it possible to suppress occurrence of follow-up lag and overshoot due to the above-mentioned response lag to thereby ensure high control accuracy.
According to the control apparatus disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2005-171893, when the predetermined update inhibiting conditions are satisfied, the update of the integral term epvnpmi is inhibited, however, if it is determined that the predetermined update inhibiting conditions are not satisfied in a state where the actual boost pressure epim is below the target boost pressure epimtrg, the update of the integral term is started from the time of the determination. In this case, the integral term is increased after start of the update of the integral term, which may result in overshoot of the actual boost pressure epim with respect to the target boost pressure epimtrg.
If the update inhibition period of the integral term is set longer so as to avoid this inconvenience, after starting the update of the integral term, the actual boost pressure epim may not reach the target boost pressure epimtrg, or to the contrary, there may occur an excessive overshoot due to causing the actual boost pressure epim to be rapidly made closer to the target boost pressure epimtrg.
To solve the above problem, it is envisaged to apply the control method disclosed in the Publication of Japanese Patent No. 4282572 to the control apparatus disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2005-171893 and calculate the feedback control term epvnpmfb appearing in Japanese Laid-Open Patent Publication (Kokai) No. 2005-171893, using the method of calculating the control input Ucain, which is disclosed in the Publication of Japanese Patent No. 4282572. More specifically, it is envisaged to calculate the feedback control term epvnpmfb as the sum of the equivalent control input Ueq and the reaching law input Urch and then add the feedback control term epvnpmfb to the basic value epbnbse of boost pressure to thereby calculate the final opening epvnfin.
However, in the case of such configuration, since the equivalent control input Ueq is calculated as a feedforward control term, as described above, mutual interference between the equivalent control input Ueq and the basic value epbnbse of boost pressure as a feedforward control term can occur, causing degradation of control accuracy. In particular, the equivalent control input Ueq has a deadbeat control characteristic, which can considerably degrade control accuracy. Further, in many cases, an actuator of a controlled object the response lag of which is large is not capable of following up changes in input required for realization of the equivalent control input Ueq, and therefore, when the equivalent control input Ueq is used to control the controlled object, an oscillating behavior or the like can be caused, which degrades control accuracy.